I'm no expert, but from what I can tell, the $600 board is only a little bigger than the DE-10. If you spend $900, you can get 256K "logic cells", which I presume are about equivalent to the DE-10's LEs. So the high end board might potentially host circuits twice as complex, but for four times the price.
Even if the board is able to do everything the DE-10 can (like the high-speed scaler), a $900 buy-in is just not going to work with hobbyists.
I think there are two major problems with anything post-2000. First, the chips are mostly too fast to replicate with FPGAs. FPGAs rarely go much past 100MHz, not nearly fast enough to duplicate chips that advanced. And then you've got the complexity barrier; those later chips are incredibly complicated. The originals took large teams years to design, so expecting hobbyists to duplicate them is probably wishful thinking.
It's pretty likely that even if FPGAs were effectively unlimited in terms of resources, we'd still be at about the limit of what hobbyists can reasonably re-implement. We're hitting multiple barriers at once: size, speed, and talent. All three would need to be fixed to do any consoles in the next generation.